1. Field Of The Invention
This invention relates to wet-type silencers for reducing the exhaust noise of water cooled internal combustion engines in which engine cooling water is mixed with the exhaust gases, such as in marine engines used to power boats.
2. Description Of The Prior Art
Wet-type exhaust systems for water cooled internal combustion engines in which the cooling water of the engine is injected into and entrained, or mixed, with the exhaust gases of the engine are old and well known for use on boats. Such exhaust systems, having a silencing unit, are typically used on highpowered speed boats.
In one prior art silencing arrangement for such exhaust systems a silencing unit having a plurality of axially spaced baffle members is located outboard of the transom of the boat. The silencer is connected in fluid flow engagement with an end portion of an engine exhaust pipe. Exhaust gases and cooling water carried by the pipe pass through a series of spaced openings which essentially define a longitudinally extending central passageway formed by axially aligned central opening in each of the plurality of axially spaced baffles. Under normal conditions a valve at the outlet end of the silencer unit is maintained open to enable the exhaust gas and water mixture to pass straight through the silencing unit, with a marginal amount of the gas/water mixture being expelled radially outward through radially outward extending spaces formed between the axially spaced baffles. When the outlet valve is in an open position, such as under high speed conditions in open water remote from residences and shore lines, the silencer is least effective in reducing noise traveling with, or caused by, the discharging exhaust gases.
When reduced sound levels are desired, or, in some areas, required by law, the valve at the outlet end of, or downstream of, the silencer is closed and substantially all exhaust gases and water are forced to flow radially outward between the axially spaced baffles to achieve maximum reduction of the exhaust sounds. Under such "closed valve" conditions the silencer or muffler causes substantial back pressure and attendant lack of power and efficiency of the engine. Also, the exhaust gas and water mixture is essentially spewed out or sprayed radially out of the exhaust silencer around the entire 360.degree. perimeter of the silencer. This arrangement allows sound waves to radiate outwardly in virtually all directions from the silencer and, due to often being used under low speed conditions, the water radiated outward from the silencer can, under adverse wind conditions, be blown onto occupants of the boat.
Additionally, known prior art commercially available wet-type silencers for such exhaust systems typically suffer from inadequate effectiveness in reducing the exhaust sound to acceptable or legal levels and/or they create unacceptably high levels of back pressure which significantly reduce the fuel efficiency and power capacity of the engine.